A civilian fatally shot a sailor aboard a docked U.S. Navy destroyer in Virginia on Monday night before he was shot dead by security forces, officials said.

The suspect had authorized access to Naval Station Norfolk, the world’s largest naval base, where he was able to wrestle a handgun from a security guard, U.S. Navy officials told NBC News.

He shot dead a sailor aboard USS Mahan, which was docked at Pier 1, before being fatally gunned down by security forces, the officials said. Both the victim and suspect were male.

The shooting happened at about 11:30 p.m. and the base was put on lockdown until around 1 a.m. while security forces responded. The Navy officials said it was not clear what sparked the incident.

To get on the base, civilians must be escorted or have a pass. Each base entrance is guarded, and all 13 piers have additional security forces. As part of ongoing security efforts, handheld ID scanners were implemented this year at Navy bases in the region, including the Norfolk station.